1. Technical Field
The technology of this disclosure pertains generally to testing of cementitious composite materials, and more particularly to a nano-engineered cementitious composite capable of self-sensing and detecting damage.
2. Background Discussion
Cementitious composites, such as concrete pavements, structural components (e.g., beams and columns in buildings), bridge superstructures, foundations, tunnels, and dams, to name a few, are susceptible to different damage modes, which are primarily caused by repeated loading, severe operating environments, and long-term deterioration. For the case of concrete pavement as an example, there is even greater concern that damage could worsen and occur more frequently with the use of heavier vehicles/trucks or new larger aircraft carrying greater payloads. The same is true for civil infrastructure construction, where cement composites are being pushed to their performance limits for construction projects involving skyscrapers, for unique and longer bridge designs, and for structures in seismically active regions.
Damage to the concrete can stem from unanticipated extreme loads, long-term degradation, fatigue, and environmental effects, among others. In fact, cracks can form in response to tension, cyclic loads (fatigue), and freeze-thaw cycles. Specifically, freeze-thaw cycles cause water in the pores of the cementitious matrix to expand (when frozen) and create new cracks or widen existing cracks. Effects such as these exacerbate damage by allowing water, air, and other chemicals to seep beneath the surface, degrade the passivation layer, and induce corrosion of steel reinforcement bars. Corrosion byproducts (or rust), like ice, take up more volume and can cause additional cracking or spalling of the concrete cover. Over time, deterioration and damage can propagate to cause catastrophic structural collapse.
Thus, detecting the onset and monitoring the progression of damage is of critical importance for facilitating necessary maintenance and for preventing catastrophic failure. For the specific case of cementitious composite structures (e.g., bridges and concrete pavements), the approaches for detecting damage can be classified as either destructive or nondestructive. A common destructive test is core sampling, in which a core sample of a specified diameter and depth is drilled and extracted from an existing concrete structure. The specimen is then subjected to laboratory tests for characterizing its mechanical properties, as well as to infer any possible deterioration occurring in the structure. While this approach provides invaluable information about the concrete structure, it has the drawback of altering the structure and potentially creating a “weak-spot” in which damage can initiate and occur in the future.
In contrast, nondestructive testing (NDT) does not alter the structure but instead utilizes technologies or methods that extract structural response data that are correlated to damage. To date, visual inspection is usually the most common NDT method employed for monitoring concrete structures. Despite its widespread use, visual inspection remains time-, cost-, and labor-intensive and can be subjective. Taking digital images of suspected damaged regions and the application of image processing techniques enable quantification of damage, but the technique is limited to surface features. On the other hand, acoustic emission (AE) is another NDT technique that uses ultrasonic transducers to characterize changes in the acoustic properties of the structure due to damage (e.g., cracks), which is mechanistically similar to impact-echo and chain dragging methods. The drawbacks of AE include its inability to detect pre-existing damage and its susceptibility to ambient noise.
Thus, it is seen above that mitigating catastrophic failure currently requires significant levels of testing in processes that are costly and often problematic.
Accordingly, a need exists for mechanisms to facilitate testing of concrete structures. The present disclosure fulfills this need and provides additional benefits in regard to various concrete structures.